ci: add cagent binary to gitignore (created by cagent-action)

Signed-off-by: David Karlsson <35727626+dvdksn@users.noreply.github.com>

Author: dvdksn

.gitignore

@@ -10,6 +10,9 @@ public
 resources
 static/pagefind
 tmp
+# Binary installed by cagent-action in CI
+cagent
+# cagent tmp files
 .cagent
 .upstream-issues.md
 .validation-log.md